1. Technical Field
The present invention relates to an image reading apparatus such as a scanner which reads an image of a document, and an image reading method.
2. Related Art
In the related art, in an image reading apparatus, a sheet feeding type device in which a transport unit which can transport a document sheet by sheet along a transport path is provided, and a document which is being transported is read by a reading unit which is disposed at a predetermined position in the middle of the transport path, and a flat-bed type device in which a reading unit provided in a carriage reads a document while the carriage moves relative to the document mounted on a document stand are known.
For example, in JP-A-2013-63843, a document reading apparatus which is provided with an ultrasonic sensor (double feeding detecting unit) which detects double feeding in which a plurality of documents are transported while being overlapped has been disclosed. The ultrasonic sensor includes an ultrasonic transmitter and an ultrasonic receiver which are disposed facing each other with a transport path of a medium interposed therebetween. In addition, there are provided in the document reading apparatus a type detecting unit which distinguishes a first medium from a second medium which is thicker than the first medium transported on the transport path and provides a type detection result, and a double feeding detecting unit which detects, based on an output of the ultrasonic sensor, whether or not there is double feeding of a medium which is transported on the transport path. An output of the ultrasonic sensor is adjusted according to the paper thickness of the document in the middle of being transported, which is detected by the type detecting unit. For example, an output intensity of the ultrasonic sensor when a transported document is a card document is adjusted so as to be stronger than that when a transported document is a paper document. For this reason, it is possible to prevent a card document from being erroneously detected as double feeding of a paper document.
Meanwhile, in the image reading apparatus of the sheet feeding type, there is a need to read an image of a booklet document, which is formed of a plurality of pages, such as a passport or a bank book, or an image of a folded document which is folded in two, such as a résumé. However, the transport unit is provided with a separating mechanism which separates, sheet by sheet, the plurality of documents which are mounted on a document support. For this reason, there is a case in which it is not possible to appropriately read an image of a booklet document or a folded document, since the image is shifted aslant, or the like, due to a force applied by the separating mechanism at the time of transportation, and which separates the document sheet by sheet. Consequently, there has been disclosed a technique in which the booklet document or the folded document is interposed in a carrier sheet formed by bonding a part of a peripheral edge portion of two colorless and transparent sheets, and an image of the document which is interposed in the carrier sheet is read without an obstruction from the separating mechanism (for example, JP-A-2008-236702, JP-A-2014-68243, JP-A-2005-260387, JP-A-2014-216998, and the like).
For example, in JP-A-2008-236702, a carrier sheet on which a transfer protocol or user identification information is present is disclosed. When reading a document by interposing the document in the carrier sheet, an image reading apparatus reads the user identification information, and reading of a document corresponding to a setting for each user based on the user identification information is performed.
In addition, in JP-A-2014-68243, JP-A-2005-260387, and JP-A-2014-216998, an image reading apparatus in which processing of combining a front face image and a rear face image, which are obtained by reading and combining both faces into one image, is performed, in a case of reading both faces by interposing a folded document in a carrier sheet is disclosed. For example, in the image reading apparatus described in JP-A-2014-68243, a position of a fold is specified by using a mark of an edge portion of a carrier sheet, and the front face image and the rear face image are combined at a position of the specified fold.
Meanwhile, in the image reading apparatus provided with the document feeding detecting unit (ultrasonic sensor) described in JP-A-2013-63843, when reading a document by interposing the document in a carrier sheet, there has been a problem in that a portion of two sheet portions of the carrier sheet is erroneously detected as double feeding of a document (for example, a paper document). For this reason, for example, there has been a need for a mechanism which performs an operation that invalidates detection of double feeding, or an operation that invalidates detection of double feeding with respect to a reading driver of a host device connected to the image reading apparatus so as to communicate therewith by operating an operation unit of the image reading apparatus. However, even when such a mechanism is added, a carrier sheet may be erroneously detected as double feeding of a paper document when a user forgets to perform an operation of invalidating detection of double feeding, and double feeding of a paper document may not be detected when reading the subsequent paper document when the user forgets to perform an operation of returning the double feeding detection to a valid state from the invalid state thereafter, which causes a failure when reading a document due to double feeding. In addition, such a problem is not limited to a sheet feeding-type image reading apparatus; approximately the same problem may occur in a flat-bed type image reading apparatus provided with an automatic document feeder which feeds a document to a document stand sheet by sheet, as an example of a transport unit.